1. Field of the Invention
The present invention relates to so-called "quick freezing" of solid materials, mainly comestibles, by direct immersion in a liquid refrigerant contained in a sealed vessel.
More specifically, the present invention deals with refrigeration immersion vessels having within their structures an elongated tunnel with movably inclined conveyor means by which solid materials are briefly conveyed through a fluid refrigerant bath of approximately minus 20 degrees Fahrenheit, while allowing no escape of refrigerant vapors from neither the vessel nor the product itself.
2. Discussion of the Prior Art
As it is perhaps well known, there are many diverse commercial, scientific and industrial applications where it is desirable to rapidly freeze materials by directly contacting them with cryogenic or refrigerant fluids, spray or vapors. In virtually all such known applications the material is essentially conveyed through an insulated tunnel of a vessel containing a preferred liquid cryogen or refrigerant, the choice of which largely being dependent on its operating temperature and the speed and degree of freezing desired.
Cryogenic fluids, such as liquid nitrogen, liquid air and liquid carbon dioxide have normal boiling points substantially below minus 100 degrees Fahrenheit, while common refrigerant fluids, such as liquid ammonia and the chlorofluorocarbons (CFC's), have boiling points above minus 100 degrees Fahrenheit and are normally utilized in the temperature range of about -20 degrees F.
In either case, however, the prior art recognizes but fails to solve a major problem of vapor containment within the various vessels as materials are treated therein or, more importantly, from the treated products themselves. Where cryogenic fluids are utilized, it is not environmentally important to contain all of the vapors, but where common refrigerants are used, it is essential that none of their vapors escape into the earth's atmosphere.
Therein lies the distinction and what is believed to be an improvement of the present invention over the prior art.
For example, in U.S. Pat. No. 3,718,284 (1973), Richardson discloses an apparatus and process for embrittling whole used automobile tires prior to crushing and grinding for recycling. This method and apparatus is typical of direct immersion art using cryogenic fluids such as liquid nitrogen, liquid carbon dioxide and liquid air, however such art does not necessarily address containment of vapors from the treated products.
A similar prior art problem of vapor containment is seen in the direct immersion of materials into FREON fluorocarbons (CFC's) as described in U.S. Pat. Nos. 3,440,831 (1969) and 3,774,524 (1973). Although the 1990 Amendments to the Clean Air Act (Title 42, United States Code, Section 7400, et.seq.) require a complete ban on using Class I CFC's by year 2000 (and Class II CFC's by the year 2030), chlorofluorocarbons and, especially CFC-12, are presently in wide use as refrigerants in many commercial applications and dichlorodifluoromethane is presently the liquid refrigerant of choice for direct immersion of comestibles because it is nontoxic, non-corrosive, colorless, odorless, nonflammable and has a boiling point of about -22 degrees Fahrenheit, all of which produces many desired results in a variety of food processing applications. For example, comestibles immersed in liquid dichlorodifluoromethane for a period of time do not stick together and have longer shelf life due to quick freezing which is known to kill bacteria. Thus, it can be easily seen that the utilization of CFC's in food processing alone has several advantages not attainable with cryogenic liquids.
Because of concerns over CFC's damage to the earth's ozone shield that screens out the sun's harmful ultraviolet rays, forty-seven countries in September 1987 agreed to the provisions of the Montreal Protocol on Substances that Deplete the Ozone Layer calling for a ban on consumption of selected CFC's and a 50 percent reduction of them by year 1999. Nonetheless, liquid CFC's are still in wide use and preferred for direct immersion of a variety of materials because of their desirable qualities.
Heretofore, however, there were no suitable immersion vessels specifically designed to contain CFC vapors as pointed out in the prior art.
First, several problem were known with sealing the entrances and exits of these vessels as materials moved in and out of them as thoroughly discussed in U.S. Pat. No. 4,175,396 (1979).
Secondly, there has also been described a persistent problem of re-condensing the voluminous gas produced as vapor in a vessel when a material at ambient temperature was immersed into a cryogenic or refrigerant bath held just below its boiling point, as discussed in U.S. Pat. Nos. 3,768,272 (1973) and 4,928,492 (1990).
Third, known immersion vessels did not specifically address the problem of cryogenic or refrigerant vapors escaping from treated materials after they exited the vessel.
These problems are addressed and solved in the present invention.